We report that ultrathin multilayered assemblies fabricated from plasmid DNA and certain synthetic polyamines undergo nanometer-scale transformations that resemble spinodal decomposition when incubated in aqueous media. The patterns and structures that are generated by this transformation are qualitatively similar to those observed for the spinodal dewetting of thin films of conventional polymers (e.g., polystyrene). However, this behavior has not, to our knowledge, been observed for this class of multilayered polyelectrolyte assemblies, for which long-range electrostatic interactions play significant roles in governing film structure and stability. We demonstrate that it is possible to promote this behavior, prevent it, or control the sizes and densities of the nanometer-scale features that result by varying the chemical structure of the polyamine, the compositions of these assemblies, or the environmental conditions to which they are exposed.

The transformations reported here permit control over the formation of nanometer-scale topography on the surfaces of objects coated with ultrathin multilayered films. This behavior could thus lead to the development of methods for the generation of nanostructure on curved or complex surfaces or on materials that are difficult to process using conventional methods. In the specific context of DNA delivery, we demonstrated recently that these multilayered films can be used to promote the localized and surface-mediated delivery of DNA to cells. The results of this current investigation suggest that these multilayered films, which are initially uniform and smooth, could be designed to transform actively upon exposure to physiological environments and present nanostructured surfaces that enhance or participate in the packaging and internalization of DNA. Experiments aimed at further elucidating the mechanism of this transformation and tailoring the resulting features will be discussed.